1. Field of the Invention
The present invention relates to a sealing and bearing arrangement in electric toothbrushes comprising a cylindrical, rotatable nose pin which has a front member on which the brush is to be mounted, a rear member with a means transmitting power from a motor, and a central member partly consisting of a thickened portion; and a hollow casing which is immobile when the nose pin rotates and which coaxially encompasses the central member, including said thickened portion, and whose front end is open, while its rear end sealingly ecompasses the nose pin, there being a clearance between the inner surface of the casing and the central member of the nose pin.
2. Description of the Prior Art
Electric toothbrushes have been on the market for many years, and a plurality of differently functioning designs have gradually been developed. However, many of these are disadvantageous in one respect or the other, e.g. by having too short a service life.
A usual incovenience is that the front member, on which the brush for brushing the teeth and the gums is mounted, is not sufficiently sealed off. Thus, foreign unwanted material, e.g. water, saliva, blood, and toothpaste ingredients, such as pumice, may penetrate into and damage the interior of the toothbrush.
Present-day electric toothbrushes with rotating brushing action comprise a casing which coaxially encompasses a central thickened portion of a rotatable nose pin which drives and rotates the brush. Between the inner surface of the casing and the outer surface of the thickened portion, there is a slide bearing space containing a lubricant. A rubber O-ring is provided in the front end of the casing to prevent foreign material from penetrating into the slide bearing space. However, the sealing action of the O-ring is inadequate. When foreign material penetrates into the slide bearing space, the friction increases, resulting in that heat is generated, the lubricant dries, and wear arises. The toothbrush simply functions so badly that it stalls from time to time and finally stops working at all. Furthermore, lubricant may escape in both directions from the leaky bearing space, and the loss of lubricant may also cause the above-mentioned inconveniences.
Another inconvenience is that the bearing of the toothbrush is not sufficiently strong to withstand the severe, differently directed loads to which it is subjected during teeth brushing. Adjacent to the rear edge of the thickened portion, an annular collar is provided around the nose pin to serve as a hold-up means for the casing and to take up axial forces. The collar is maintained in place by an annular bronze plate arranged around the nose pin, adjacent to the rear edge of the collar. The contact between the collar and the casing has a certain braking effect with ensuing wear. Also, the friction between the mutually adjacent surfaces of the collar and the bronze plate contributes to this braking effect and ensuing wear. The wear also entails a disagreeable squeaking noise and gradually impairs the function of the bearing.
Consequently, there is need for an electric toothbrush with rotating brushing action, which is sealed against unwanted materials and which is mounted in bearings adapted to take up considerable forces in all directions.